Finite element analysis of four-abutment Hader bar designs

Three-dimensional finite element analyses were conducted on the four-abutment Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three stiffener heights (1, 2, and 3 mm) were analyzed representing a clinical range of usage. Three material types were studied which represent a selection of alloys commonly used clinically. The model consisted of a representative Hader bar of 1.8-mm diameter with a 1-mm inferior stiffener. The ends of the bar were fixed to a 5-mm diameter coping which was attached to a 3.8-mm root form-type implant fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200 Newton occlusal force was imposed on the mesial bar and a 450 Newton force on the distal bar for the three stiffener heights. The results of these analyses predicted yielding and fracture (failure) for all 1-mm stiffener height and type IV gold alloy cases studied. Stiffener height was found to play a strong role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. Factors of safety with respect to static yield strength ranged from 1.44 to 2.12 on the distal portion.